The generation of current in vessels is normally carried out using a generator connected to a battery. The generator is driven by the vessel's combustion motor and charges the battery. During operation of the vessel, there is a continual charging of the battery, while at the same time power is provided for the vessel's electronics. When the combustion motor is switched off, the battery, which has a limited amount of available power, is used to provide current for the electronics.
In order to generate alternating current for alternating current applications in the vessel, a DC/AC transducer, or inverter, is used to convert the direct current voltage of the battery to an alternating current voltage of a certain frequency.
Alternating current applications, for example alternating current motors with large starting torque, can require a lot of current. Such an application can, for example, be a compressor in a refrigeration system. When the alternating current motor is started, large starting currents are required. A single-phase alternating current motor can have a current requirement when it starts that is four to eight times the current requirement in normal operation. This creates a number of problems.
For example, the starting current requirement must be taken into account when selecting the inverter. A standard inverter which can drive a motor of 1 kW, that is which is rated at 1 kW, will not manage to start an alternating current motor with high starting torque. It may be the case that an inverter rated at 2 kW is required in order to start the motor, which in turn means that an unnecessarily large and expensive inverter is used during normal operation when the alternating current motor draws normal current.
Another problem is that the high starting currents can jeopardize the other electronics in the vessel, which are electronics that can be vital for being able to operate the vessel in a safe way. That is to say, if the alternating current application draws too large currents, the voltage across the battery can drop so that other electronics can not be supplied with current. This is, of course, a situation that must not arise.
WO 01/89070 describes a circuit in a vehicle. When the battery voltage drops below a certain level, the circuit increases the voltage up to the voltage required by the load.